EP2373235B1

EP2373235B1 - Force sensing distal femoral alignment system

Info

Publication number: EP2373235B1
Application number: EP09824192.0A
Authority: EP
Inventors: Barjinder Singh Chana; Michael G. Fisher; Michael Haight; Leo Beckers
Original assignee: Synvasive Technology Inc
Current assignee: Synvasive Technology Inc
Priority date: 2008-10-30
Filing date: 2009-10-30
Publication date: 2016-05-04
Anticipated expiration: 2029-10-30
Also published as: US20100198275A1; EP2373235A4; US9980735B2; WO2010051490A1; EP2373235A1; US20150230804A1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional of, and claims the benefit of priority under 35 U.S.C. $ 119(e), U.S. Provisional Application No. 61/109,770 (Attorney Docket No. 021976- 000900US) filed October 30, 2008.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to medical surgical systems. More specifically, the invention relates to systems for facilitating knee surgery procedures, in particular, knee replacement procedures.
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint, the soft tissues including the ligaments of the knee. The knee is generally divided into three compartments: medial (the inside part of the knee), lateral (the outside part of the knee), and patello-femoral (the joint between the kneecap and the femur). The medial compartment comprises the medial joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The lateral compartment comprises the lateral joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The patellofemoral compartment comprises the joint between the undersurface of the kneecap or patella and the femur. Four ligaments are especially important in the stability, alignment and functioning of the knee-the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia is often worn away, allowing the femur to directly contact the tibia. This bone-on-bone contact can cause significant pain, discomfort, and disability for a patient and will often necessitate knee replacement or knee arthroplasty.
Knee arthroplasty involves replacing the diseased and painful joint surface of the knee with metal and plastic components shaped to allow natural motion of the knee. Knee replacement may be total or partial. Total knee replacement surgery, also referred to as total knee arthroplasty ("TKA"), involves a total replacement of the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts. Cuts are made on the distal end of the femur and the proximal end of the tibia. Prosthetic parts are then attached. The prosthetic parts create a stable knee joint that moves through a wide range of motion. The replacement of knee structures with prosthetic parts allows the knee to avoid bone-on-bone contact and provides smooth, well-aligned surfaces for joint movement.
In knee replacement surgeries, it is often vital to restore the mechanical alignment of the knee, i.e., the proper alignment of the mechanical axes of the femur and tibia with each other. Many methods and devices currently are used to restore the mechanical alignment of the leg. These methods and devices are typically used during Total Knee Replacement surgery and include alignment rods, e.g., intramedullary and extramedullary rods, surgical navigation systems, and CT and or MRI based "bone morphing" or 'shape-fitting" technologies. Generally, empirical anatomical landmarks are used in these methods. These anatomical landmarks are either directly/mechanically observed intra-operatively, or indirectly relied upon, serving as the foundation of a computer generated reference method. Reference geometry and physical or virtual measurements are often used to ultimately align bone-cutting guides or templates which facilitate bone resections (made with a surgical saw blade). These bone resections will typically properly orient a knee prosthesis in the correct location/alignment. Generally, none of these methods directly take the condition or tendencies of the soft-tissue structures, such as the lateral collateral and medial collateral ligaments, about the knee into consideration.
Historically, surgeons performing total knee replacement surgery in the late 1970s and early 1980s, would typically first resect the proximal tibia, creating a flat surface perpendicular to the shaft of the tibia. The leg was then brought to extension. Spacer blocks were shoved between the resected tibia and the uncut distal femur. The spacer blocks were selected from various thicknesses in order to distract the knee joint space to the extent the ligaments about the knee were somewhat taut. Once the knee joint was distracted to that taut condition, a distal femoral cutting guide was positioned in a way to yield a distal femoral bone cut parallel to the tibial cut. It was believed then, a distal femoral bone cut using this method of distracting the joint space between the tibia and femur, would yield proper alignment of the mechanical axis of the leg. This method would often prove successful as practiced by a skilled surgeon and in the case of "passive deformities" of the knee. However, the distraction method would typically not have any accurate means of determining ligament forces between the medial side of the knee and/or the lateral side of the knee. As such, proper alignment would often not be restored. Additionally, the method of first making a proximal tibial bone resection and then making a distal femoral bone resection parallel to the tibial bone resection did not restore proper alignment of the leg in the case of "fixed deformities" of the knee. The case of "fixed deformities" of the knee would otherwise require ligament releases to restore proper alignment of the knee. Accordingly, many early knee replacement surgeons determined the tibial bone resection and the distal femoral bone resections should be made independent of each other.
As technology has advanced, including the introduction of CT scanners and MRI technology, the thought of computerized bone morphing has gained popularity as a means to accurately place cutting guides. The cutting guides in turn would be used in efforts to place prosthetic knee implants in a position in which the knee is properly aligned. Early studies have not found these bone morphing technologies always accurate, reporting proper alignment of the leg was not restored. However, a proper patient selection, e.g., patients with mild, passive deformities of the knee, might be viable candidates for bone morphing technology, assuming those patients/deformities could be properly corrected by simple anatomical referencing, as determined by a CT or MRI scan.
However, bone morphing technology is often costly, requiring a CT or MRI scan to determine any given patient's anatomy. Electronic images from such scans must be "filtered" by a computer technician. The "filtered" scan data must be electronically conveyed to some type of fabrication machine, such as a CNC Machining Center or a Rapid Prototype Machine. Ultimately, "shape-matching" and "patient specific" cutting guides must be produced and delivered into surgery.
As such, there is a clear need for systems, devices, and methods of knee surgery that can help surgeons quickly, accurately, and cost-effectively position the distal femoral cutting guide, thus restoring proper alignment and soft-tissue balance of the leg during total knee replacement surgery.

2. Description of Background Art

Non-patent literature which may be of interest may include: Murray, David G., "Variable Axis(TM) Total Knee Surgical Technique," Howmedica Surgical Techniques, Howmedica Inc. 1977; Mihalko, WH et al., "Comparison of Ligament-Balancing Techniques During Total Knee Arthroplasty," JnI. Bone & Jt. Surg., Vol. 85-A ; Eckhoff, D G et al., "Three-Dimensional Morphology and Kinematics of the Distal Part of the Femur Viewed in Virtual Reality, JnI. Bone & Jt. Surg., Vol. 85-A ; and Ries, M D, et al., "Soft-Tissue Balance in Revision Total Knee Arthroplasty," JnI. Bone & Jt. Surg., Vol. 85-. Patents of interest may include U.S. Patents Nos. 4,501,266 ; 4,646,729 ; 4,703,751 ; 4,841,975 ; 5,116,338 ; 5,417,694 ; 5,540,696 ; 5,597,379 ; 5,720,752 ; 5,733,292 ; 5,800,438 ; 5,860,980 ; 5,911,723 ; 6,022,377 and 6,758,850 . Patents applications of interest may include co-assigned U.S. Patent Applications Nos. 10/773,608 , now U.S. Patent No. 7,442,196 , entitled "Dynamic Knee Balancer" (Attorney Docket No. 021976- 000200US); 10/973,936 , now U.S. Patent No. 7,578,821 entitled "Dynamic Knee Balancer with Pressure Sensing" (Attorney Docket No. 021976-000210US); 11/149,944 now U.S. Patent Publication Application No. 2005/0267485 A1 entitled "Dynamic Knee Balancer with Opposing Adjustment Mechanism" (Attorney Docket No. 021976-000220US); 61/090,535 entitled "Sensing Force During Partial and Total Knee Replacement Surgery" (Attorney Docket No. 021976-000800US); and 61/107,973 entitled "Dynamic Knee Balancing for Revision Procedures" (Attorney Docket No. 021976-000700US).
US 2007/0244488 describes a tensor for use with a surgical navigation system. The tensor comprises a first bone engaging member engageable with a first bone and a second bone engaging member engageable with a second bone. A force-applying mechanism is confirmed to forcibly move the first and second bone engaging members relative to one another and a sensor detects the value of the force applied by the force-applying mechanism. A transmitter communicates a parameter associated with the tensor to the surgical navigation system.
US 2005/0267485 describes a device for performing a surgical procedure on a knee comprising a stationary femoral member attachable to the distal femur, an adjustable femoral member moveable coupled with the stationary member to address tension in at least one ligament of or adjacent the knee and an adjustment mechanism coupled to the assembly.
US 5,213,112 describes a tension meter for orthopaedic surgery for measuring the degree of tension between bones.

BRIEF SUMMARY OF THE INVENTION

The present invention is set out in the appended claims. Described herein are devices, systems, and methods for facilitating a surgery performed on a knee, particularly by facilitating the aligning of the knee during a total knee replacement surgery. A femoral assembly is engaged with a distal femur and placed in the gap between the distal femur and proximal tibia. The femoral assembly comprises a stationary portion, an adjustable medial portion, and an adjustable lateral femoral portion. The positions of the medial and lateral femoral portions relative to the stationary portion can be separately adjusted to adjust the varus-valgus alignment of the knee, e.g., the angle between the femur and tibia, as well as the tension in the soft tissues adjacent the knee. Additionally, the femoral assembly comprises adjustable posterior members that fill the posterior capsule of the knee with a thickness similar to the prosthetic femoral implant. Typically, a force sensor will be provided to sense the forces in the medial portion of the knee and the lateral portion of the knee, and the medial and lateral femoral portions will be adjusted so that the sensed forces are balanced. A visual display may be provided to show the surgeon the sensed forces. In addition, a thickness adapter may be provided to removable attach to the force sensor to fill the space between the femur and tibia to the point force readings are obtained. The alignment of the knee can be visually verified using a knee alignment verification member coupled to the femoral assembly, and further verified by angular graduation markings placed upon the femoral stationary portion. The knee alignment verification member may emit laser beams along the mechanical axes of the femur and tibia. Or, alignment rods which align along the mechanical axes of the femur and tibia may be coupled to the knee alignment verification member. The alignment of the knee can be verified using with the laser beams and/or the alignment rods. When the knee is properly aligned, placement pins may be positioned in the distal femur guided by the femoral assembly. The femoral assembly can then be removed and a cutting guide can be positioned on the distal femur based on the position of the placement pins. A cut parallel to a previously made cut on the tibia can then be made on the distal femur. A prosthetic knee placed on these cuts will maintain the proper alignment of the knee.
Described herein is a system for aligning the knee during a surgical procedure on the knee. The system comprises a femoral assembly that is removably engaged with a distal femur. The femoral assembly includes a stationary femoral portion, an adjustable medial femoral portion (which is coupled to the stationary femoral portion), and an adjustable lateral femoral portion (which is coupled to the stationary femoral portion. A knee alignment verification member is coupled with the stationary femoral portion of the femoral assembly and provides visual confirmation of a femoral and tibial mechanical axes of the knee. A force sensor is coupled with the stationary femoral portion of the femoral assembly. The force sensor comprises a medial portion for sensing a first force in a medial portion of the knee and a lateral portion for sensing a second force in a lateral portion of the knee.
In one embodiment, the knee alignment verification member means includes a laser knee alignment verification member is coupled to the stationary femoral portion. The laser knee alignment provides a first laser beam oriented along the femoral axis of the knee and a second laser beam oriented along the tibial axis of the knee.
In some embodiments, the knee alignment verification member includes a mechanical knee alignment verification assembly. The mechanical knee alignment verification assembly includes a knee alignment hub. A first rod is coupled with the knee alignment hub to be oriented along the femoral axis of the knee and a second rod is coupled with the knee alignment hub to be oriented along the tibial axis of the knee.
In an embodiment, the adjustable medial portion includes a medial paddle and the adjustable femoral portion includes a lateral paddle.
In still other embodiments, the position of the adjustable medial femoral portion relative to the stationary femoral portion is adjustable. The position of the adjustable lateral femoral portion relative to the stationary femoral portion is adjustable.
In other embodiments, the adjustable medial femoral portion and the adjustable lateral femoral portion are separately adjustable.
In some embodiments, a medial rotatable screw couples the adjustable medial femoral portion with the stationary femoral portion. A lateral rotatable screw couples the adjustable lateral femoral portion with the stationary femoral portion.
In some embodiments, rotating the medial rotatable screw adjusts the position of the adjustable medial femoral portion relative to the stationary femoral portion. Rotating the lateral rotatable screw adjusts the position of the adjustable lateral femoral portion relative to the stationary femoral portion.
In some embodiments, the force sensor comprises a force sensing element selected from the group consisting of piezoelectric sensors, force sensing resistors, force sensing capacitors, strain gages, load cells, and pressure sensors.
In still other embodiments, a processor is coupled with the force sensor for processing sensed force data into usable data and for providing the data to a user. A visual display is coupled with the processor and adapted to display the usable data.
In some embodiments, the visual display displays usable data representing a first force sensed in the medial portion of the knee and a second force sensed in the lateral portion of the knee.
In some embodiments, the system for aligning a knee during knee surgery includes a plurality of locating pins. The stationary femoral portion defines at least one medial aperture for positioning at least one locating pin on the distal femur and at least one lateral aperture for positioning at least a second locating pin on the distal femur.
In some embodiments, a cutting guide is removably engaged with the distal femur. The cutting guide is positioned relative to the distal femur based on the position of at least one first locating pin and the at least a second locating pin.
In some embodiments, the force sensor is removably coupled to a thickness adapter. The adapter fills the space between the femur and tibia.
In some embodiments, the adjustable medial femoral portion and the adjustable lateral femoral portion include a medial fulcrum and lateral fulcrum. The fulcrums are positioned against the provisionally cut distal femur when the distal femoral alignment assembly is mounted against the distal femur. In other embodiments, a bone interface plate is disposed between the fulcrums and the distal femur.
Described herein is a method for aligning the knee during a surgical procedure on the knee including engaging a femoral assembly with a distal femur. The femoral assembly includes a stationary femoral portion, an adjustable medial femoral portion (coupled to the stationary femoral portion), and an adjustable lateral femoral portion (coupled to the stationary femoral portion). A force sensor is coupled with the stationary femoral portion of the femoral assembly. A first force is sensed in a medial portion of the knee and a second force is sensed in the lateral portion of the knee using the coupled force sensor. The position of the adjustable medial femoral portion can be adjusted separately relative to the stationary femoral portion based on the sensed first and second forces to align a femoral and tibial mechanical axes of the knee. Te alignment of the femoral and tibial mechanical axes of the knee are visually confirmed using a knee alignment verification assembly coupled with the stationary femoral portion of the femoral assembly.
In one example, a method for aligning the knee during a surgical procedure on the knee comprises coupling a mechanical knee alignment verification assembly with the stationary femoral member of the femoral assembly. A first alignment rod of the mechanical knee alignment verification assembly is aligned along the femoral axis of the knee and a second alignment rod of the mechanical knee alignment verification assembly is aligned along the tibial axis of the knee. The femoral and tibial mechanical axes of the knee is visually confirmed by the alignment of the first alignment rod and the second alignment rod relative to each other.
In another example, a laser knee alignment verification member is coupled with the stationary femoral member of the femoral assembly, A first laser beam from the laser knee alignment verification member is aligned along the femoral mechanical axis of the knee and a second laser beam from the laser knee alignment verification member is aligned along the tibial mechanical axis of the knee along the tibial axis of the knee, The alignment of the femoral and tibial mechanical axes of the knee is visually confirmed by the alignment of the first laser beam and the alignment of the second laser beam relative to each other.
In some examples, the positions of the adjustable medial femoral portion relative to the stationary femoral portion and of the adjustable lateral femoral portion relative to the stationary femoral portion are adjusted based on the sensed first force and the sensed second force so that the first and second forces are balanced.
In some examples, the first force in a medial portion of the knee is sensed and a second force in a lateral portion of the knee is sensed using the coupled force sensor. This includes transmitting a voltage to a sensor element of a thin force sensing portion of the force sensor and measuring the voltage after it has passed through the sensor element. The percentage of the voltage that passed through the sensor element is determined relative to the voltage transmitted to the sensor element. The measured force is derived from the percentage.
In yet another example, the sensed first force and the sensed second force visually displayed by a display coupled to the force sensor.
In some examples, separately adjusting the position of the adjustable medial femoral portion relative to the stationary femoral portion and the position of the adjustable lateral femoral portion relative to the stationary femoral portion comprises rotating at least one of a lateral rotatable screw coupling the adjustable lateral femoral portion to the stationary femoral portion and a medial rotatable screw coupling the adjustable medial femoral portion to the stationary femoral portion.
In some examples, the stationary femoral portion defines at least one medial aperture and at least one lateral aperture. The method further includes positioning at least one locating pin on the distal femur based on at least one medial aperture and positioning at least a second locating pin on the distal femur based on the at least one lateral aperture.
In an examples, the femoral assembly is disengaged with the distal femur and engages a distal femoral cutting guide with the distal femur. The distal femoral cutting guide is positioned relative to the distal femur based on the position of at least one first and at least one second locating pins.
In some examples, cuts are made on the distal femur based on the position of the distal femoral cutting guide.
Described herein is a method for aligning a leg during knee surgery. The leg has a femur and a tibia. The femur has a mechanical axis, a distal end and a proximal end. The tibia has a mechanical axis, a distal end and a proximal end. The method of aligning the leg includes engaging a femoral assembly with the provisionally cut distal end of the femur. The femoral assembly includes a stationary femoral portion, an adjustable medial femoral portion that has a medial pivot fulcrum coupled to the stationary femoral portion, and an adjustable lateral femoral portion that has a lateral pivot fulcrum coupled to the stationary femoral portion. A force sensor is coupled with the stationary femoral portion of the femoral assembly. A medial posterior member is reversibly coupled to the medial side of the stationary femoral portion. A lateral posterior member is reversibly coupled to the lateral side of the stationary femoral portion. The medial member abuts the medial posterior femur and the lateral member abuts the lateral posterior femur. A first force is sensed in a medial portion of the knee and a second force is sensed in the lateral portion of the knee using the force sensor. The position of the adjustable medial femoral portion is adjusted relative to the stationary femoral portion and the position of the adjustable lateral femoral portion is (separately) adjusted relative to the stationary femoral portion based on the sensed first and second forces to align the femoral and tibial mechanical axes of the knee. The alignment of the femoral and tibial mechanical axes of the knee is visually confirmed using a knee alignment verification assembly which is coupled with the stationary femoral portion of the femoral assembly.
In one example, the medial member abuts the medial posterior femur and the lateral member abuts the lateral posterior femur when the leg is fully extended.
In some examples, the medial and lateral fulcrums determine fixed distance points to adjust an angle.
In some examples, a bone interface plate is disposed between the adjustable medial and lateral femoral portions and the distal femur.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an exploded view of a distal femoral alignment component assembly.
Figure 2 shows a top view of the unadjusted distal femoral alignment assembly of Figure 1.
Figure 3 shows a top view of the adjusted distal femoral alignment assembly of Figure 1.
Figure 4 shows a perspective view of the unadjusted distal femoral alignment assembly of Figure 1.
Figure 5 shows a perspective view of the adjusted distal femoral alignment assembly of Figure 1.
Figures 6 and 7 shows perspective views of a knee alignment system.
Figure 8 shows a visual display of a knee alignment system.
Figures 9-10 show a side view of a knee alignment system, including the distal femoral alignment component and the force sensor coupled together, being placed in the gap.
Figures 11-12 show a perspective view of a knee alignment system, including the distal femoral alignment component and the force sensor coupled together, being placed in the gap.
Figures 13-23 show a method of aligning a knee during surgery.
Figure 24 A-B shows exploded views of a knee alignment system.
Figure 25 shows a top view of the unadjusted distal femoral alignment assembly.
Figures 26A and 26C show perspective posterior views of the unadjusted distal femoral alignment assembly shown in Figure 25.
Figure 26B shows a posterior perspective of the unadjusted distal femoral alignment assemblies shown in Figures 26A and 26C with the bone interface plate removed.
Figures 27-35 show an alternative method of aligning a knee surgery.
Figure 36 is a flow chart schematically illustrating a method for aligning and balancing a knee during knee surgery.

DETAILED DESCRIPTION

Described herein are systems, devices, and methods for facilitating the alignment and balancing of the knee during knee replacement surgery and verifying such balance and alignment. Once the knee is properly aligned, a cut parallel to a previously made cut on the tibia can be made on the distal femur. A prosthetic knee placed on these cuts will maintain the proper alignment of the knee.
Referring now to Figure 1 , a distal femoral alignment assembly or component 100 is shown in an exploded view. As shown in Figure 1 , distal femoral alignment assembly 100 can be used for either the left or right knee, i.e., one side of the distal femoral alignment assembly may be the medial side while the other is the lateral side and vice versa. Distal femoral alignment assembly 100 comprises a main body 101, an adjustable medial femoral portion coupled to the main body, and an adjustable lateral femoral portion coupled to the main body. When the distal femoral alignment assembly 100 is coupled to a distal femur, the main body or stationary portion of the distal femoral alignment assembly is generally stationary with respect to the adjustable medial and lateral femoral portions. The adjustable medial and lateral femoral portions are adjusted with respect to the main body.
Adjustable medial and lateral femoral portions respectively comprise medial and lateral paddles 102, 103. The medial and lateral paddles each comprise anti-rotation shafts 104, 105 which fit into slots 106 of the main body. Medial and lateral distraction screws 107, 108 respectively couple the medial and lateral paddles 102, 103 with the main body 101. Distraction screw capture pegs 109, 110 fix the axial position of the distraction screws 107, 108 relative to the main body 101 such that rotation of the medial and lateral distraction screws only adjusts the positions of the adjustable medial and lateral femoral portions with respect to the main body 101. The main body comprises mounts for attachment of a force sensor 111.
Referring now to Figure 2, the main body 101 of the distal femoral adjustment assembly 100 further defines cutting guide locating apertures on its medial 113a-c and lateral 112a-c sides. These apertures are cutting guide locating means, e.g., by facilitating the placement of placement pins from which provide points of reference for the placement of a cutting guide. The main body further defines slots or verification attachment slots or apertures 114a, 114b for attaching a knee alignment verification means as described below.
Figures 2 and 4 show the distal femoral adjustment assembly 100 unadjusted. Figures 3 and 5 show the distal femoral adjustment assembly 100 adjusted, i.e., the position of one paddle of the distal femoral adjustment assembly has been moved relative to the other.
Figures 6 and 7 show a perspective view of a knee alignment system 99a. The system comprises the distal femoral adjustment assembly 100 as described above. The system further comprises a electronic force-sensing means or force sensor 115 coupleable with the distal femoral adjustment assembly 100. As shown, the force sensor 115 comprises a handheld tool but may alternatively be a smaller device coupleable with the main body of the distal femoral adjustment assembly 100. The force sensor 115 senses the force between the medial portion of the distal femur and the medial portion of the tibial plateau as well as the force between the lateral portion of the distal femur and the lateral portion of the tibial plateau, for example, by comprising first and second force sensing portions 116a, 116b, the first force sensing portion 116a being a lateral force sensing portion while the second 116b is a medial force sensing portion and vice versa. The distal femur and tibial plateau are not shown in Figs. 6-7. The force sensor 115 may be similar to those described U.S. Patent Applications Nos. 61/090,535 entitled "Sensing Force During Partial and Total Knee Replacement Surgery"
(Attorney Docket No. 021976-000800US) and 61/107,973 entitled "Dynamic Knee Balancing for Revision Procedures" (Attorney Docket No. 021976-000700US).
Figure 8 shows a visual display 117 coupleable with the force sensor 115. The visual display displays data representative of the force sensed by the force sensor and may be similar to those described in U.S. Patent Applications Nos. 10/973,936 , now U.S. Patent No. 7,578,821 , entitled "Dynamic Knee Balancer with Pressure Sensing" (Attorney Docket No. 021976- 000210US); 61/090,535 entitled "Sensing Force During Partial and Total Knee Replacement Surgery" (Attorney Docket No. 021976-000800US); and 61/107,973 entitled "Dynamic Knee Balancing for Revision Procedures" (Attorney Docket No. 021976-000700US).
Figures 9-23 show a method of using an exemplary knee alignment system during knee replacement surgery. As shown in Figures 9 and 11, the force sensor 115 is coupled to the distal femoral alignment assembly 100. As shown in Figures 10 and 12, the distal femoral alignment assembly 100 and the coupled force sensor 115 are placed in the gap 120 between the distal femur 118 and the tibial plateau 121 of the knee. As shown in Figure 13, the force sensor 115 senses the forces between the lateral and medial portions of the distal femur and the tibial plateau. The visual display 117 shows the sensed forces (as an example, the display shows the forces unbalanced). An adjustment wrench 122 is coupled to a rotatable distraction screw 107 of the distal femoral alignment assembly 100. As shown in Figure 14, when the unadjusted distal femoral alignment assembly 100 and the coupled force sensor 115 are first placed in the gap 120 between the distal femur 118 and the tibial plateau 121, the knee may be misaligned, i.e., the femoral axis and the tibial axis are not aligned with each other as in a normal knee. As shown in Figure 14, when the unadjusted distal femoral alignment assembly 100 and the coupled force sensor 115 are first placed in the gap 120 between the distal femur 118 and the tibial plateau 121, the knee may be misaligned, i.e., the femoral axis and the tibial axis are not aligned with each other as in a normal knee. As shown in Figure 14, the bottom surface of the distal femoral alignment assembly is 80° relative to the mechanical axis 123 of the femur 118. As shown in Figure 15, at least one of the rotatable screws 107, 108 is rotated with the adjustment wrench 122 to adjust the relative position of the adjustable medial and/or femoral portions and to correct the alignment of the knee. Generally, by balancing the sensed forces in the medial and lateral portions of the knee, correct alignment of the knee can be achieved (as shown in the visual display). For example, as shown in Figure 16, the distal femoral alignment assembly 100 has been adjusted so that the bottom surface of the distal femoral alignment assembly is 85° relative to the mechanical axis 123 of the femur 118.
The system will typically further comprise a knee alignment verification means to verify the alignment of the knee by verifying the angle formed by the mechanical axes of the femur and tibia. As shown in Figures 17 and 18, the knee alignment verification means may be a laser knee alignment verification member 124 coupleable to the main body of the distal femoral alignment member 100. As shown in Figure 18, the laser knee alignment verification member 124 emits a femoral laser beam 125a to be aligned along the mechanical axis 123a of the femur and a tibial laser beam 125b to be aligned along the mechanical axis 123b of the tibia. The angle of the femoral laser beam and the tibial laser beam relative to each other can be used by the surgeon to verify the proper anatomical alignment of the knee, i.e., the angle between the mechanical axes 123a, 123b of the femur and tibia. Alternatively, as shown in Figures 19 and 20, the knee alignment verification means may be a mechanical knee alignment verification assembly 126. The mechanical knee alignment verification assembly 126 comprises a mechanical knee alignment verification hub 127, a femoral alignment rod 128 coupleable with the hub 127, and a tibial alignment rod 129 coupleable with the hub 127. The coupled femoral alignment rod 127 can be aligned along the mechanical axis 123a of the femur 118. The coupled tibial alignment rod 129 can be aligned along the mechanical axis 123b of the tibia 119. The angle of the femoral alignment rod 128 and the tibial alignment rod 129 relative to each other can be used by the surgeon to verify proper alignment of the knee.
As shown in Figure 21, the system may further comprise a plurality of locating pins 130a, 130b. When the knee is properly aligned, at least one locating pin (130a and/or 130b) may be placed on the medial side of the distal femur 118 and at least one locating pin may be placed on the lateral side of the distal femur as guided by the apertures of the distal femoral alignment assembly. As shown in Figure 22, once the locating pins 130a, 130b are placed on the distal femur 118, the distal femoral alignment assembly 100 may be disengaged from the distal femur.
As shown in Figure 23, the system may further comprise a distal femoral cutting guide 131 which can be coupled to the distal femur 118 and positioned based on the position of the locating pins 130a, 130b. Cuts are made on the distal femur 118, for example, with a surgical saw blades 132. Typically, these cuts will form the basis for positioning of the femoral portion of an artificial knee. Exemplary surgical saw blades which may be used to make these cuts on the distal femur are described co-assigned U.S. Patents Nos. 6,022,353 ; 6,503,253; and 6,723,101 .
Referring now to Figures 24A-B, an alternative distal femoral alignment system 99b is shown including cutting guide 131 for making a provisional cut on the distal femur in order to mount the distal femoral alignment assembly 100 flush against the provisionally cut distal femur. As shown in Figure 25, angular graduation marks 133 are provided. The graduation marks correspond to movement created by adjusting either the medial or lateral distraction paddles 102, 103 as shown in Figure 26B. For clarity purposes, a right distal femur is shown in Figs. 27-28 and 34-35 and a right knee joint with femur and tibia is shown in Figures 29-33. The medial side of components or assemblies of the distal femoral alignment system shown in Figure 24 are hereby described either medial or lateral based on their position when used on a right knee. Of course, the invention can be used on the left and/or right knees. Convex shaped pivot fulcrums 500a, 500b are provided on the surfaces of the distraction paddles 102, 103 which directly contact the provisionally cut distal femur when the distal femoral alignment assembly 100 is mounted against the distal femur 118. The curved surface of the distraction paddles 102, 103 creates fixed distance fulcrum points to determine how much angle is being adjusted. Figures 26A and 26C show another embodiment of the distal femoral alignment assembly 100 of the alternative distal femoral alignment system 99b shown in Figure 24, which includes bone interface plate 137. This plate 137 provides protection from convex shaped distraction paddles 102 and 103 from indenting the softer cancellous bone exposed as a result of a provisional cut being made on the distal femur 118 (not shown in Fig. 26). Figure 26C shows the bone interface plate 137 sitting on top of convex shaped distraction paddles 102 and 103 in their unadjusted position. Shoulder screw 138 is shown, which slips through a loosely fitted hole 139 in bone interface plate 137 to allow for tilting of bone interface plate 137 when convex shaped distraction paddles 102 and 103 are adjusted from their unadjusted position to an adjusted position. Spacing between convex shaped adjustment paddles 102 and 103 is maintained in the medial-lateral direction to provide for a known pivot fulcrum between the two convex shaped adjustment paddles, which corresponds to angular graduations 133 shown in Figure 25. The angular gradations provide an indication of the angle between the femur and tibia
Referring now to Figures 27-35, a method of using an exemplary knee alignment system used during knee replacement surgery is shown. For purposes of clarity, a bone cut has already been made on the proximal tibia 119 prior to the methods described in Figures 27-35. Figure 27 shows provisional distal femoral cutting guide 131 moveably attached to the provisionally cut distal femur 118 via two pins 130a and 130b. Figure 28 shows provisional femoral cutting guide 131 and pins 130a and 130b now having been removed and femoral anterior-posterior cutting guide 134 is now removably attached to distal femur 1 18. Saw blade 132 is shown and the anterior and posterior bone cuts are performed on distal femur 118. Figure 29 shows now the "extension gap" with the proximal tibial cut having been made and a provisional distal femoral cut having been made. The posterior femoral cut has also been made but hidden from view in Figure 29. The anterior cut has also been made on distal femur 118.
Moving now to Figure 30, the distal femoral alignment assembly 100 and other components of the distal femoral alignment system 99b are shown between the proximal tibia 119 and the distal femur 118, with the leg in full extension. Thickness adapter 133 is shown moveably coupled to force sensor 115, and force sensor 115 is moveable coupled to distal femoral assembly 100. Adjustable posterior member 135a is shown adjacent to a longitudinal slot 400 open on the posterior side of distal femoral assembly 100, with the slot closed on the anterior side of the distal femoral assembly 100. Figure 31 shows adjustable posterior member 135a having now been moveably coupled within the longitudinal slot 400 along the medial side
of distal femoral assembly 100. Moveable coupling means 136a, 136b can include magnets or other common coupling means such as screws or spring clips. Longitudinal slots are also provided on the opposite side of the distal femoral assembly 100. Longitudinal slots along the sides of distal femoral assembly 100 are of adequate length to allow for anterior-posterior adjustment of adjustable posterior member to abut the previously made posterior cut 401 of the distal femur 118. The adjustable posterior members further balance extension filling the posterior space with a condylar thickness similar to the posterior condylar thickness of the femoral component to be implanted thus taking into account soft-tissue tendancies, or bias. Figure 32 shows components and assemblies of the distal femoral alignment system 99b now completely in place between the proximal tibia and the distal femur and force readings coupled from force sensor 115 are being displayed on display 117, It is understood that display 117 may be integral to force sensor 115. The display 117 can also be separable from the sensor. The display 117 is showing force readings of 5 and 2 lateral and medial respectively, indicating lower force between the medial side of the distal femur and the medial side of the proximal tibia, in this example. Adjustment wrench 122 is shown in line with the medial distraction screw 107. Figure 33 shows the medial distraction paddle 102 having now been adjusted to a point wherein the forces being measured by sensor 115 and displayed by display 117 read 5 on both the lateral and the medial side. Pin 130a is shown being driven through a lateral side cutting guide locating aperture and pin 130b has yet to be driven through the medial side cutting guide locating aperture. Figure 34A shows both pins having now been driven through cutting guide locating apertures of distal femoral assembly 100, and distal femoral assembly 100 now having been removed from the distal femur 118. Cutting guide 131b is positioned over pins 130a and 130b. Figure 34B shows cutting guide 131 b now positioned over pins 130a and 130b and saw blade 132 will be used to make the final distal femoral cut at an angle "A" which is the plane of balanced resection as determined by the force sensor. Figure 35 shows femoral anterior-posterior cutting guide 134 now removably coupled to distal femur 118 and saw blade 132 is shown making a final cut on the anterior distal femur. Anterior and posterior chamfer cuts will also be made on the distal femur 118 at this point.
While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting in scope of the invention which is defined by the appended claims.

Claims

A system for aligning the knee during a surgical procedure on the knee, the system comprising:
a femoral assembly (100) removably engagable with a distal femur, the femoral assembly including a stationary femoral portion (101), an adjustable medial femoral portion (102) coupled to the stationary femoral portion, and an adjustable lateral femoral portion (103) coupled to the stationary femoral portion;

a knee alignment verification member (124; 126) coupleable with the stationary femoral portion (101) of the femoral assembly and providing visual confirmation of a relationship of femoral and tibial mechanical axes of the knee ; and

a force sensor (111) coupleable with the stationary femoral portion (101) of the femoral assembly, the force sensor comprising a medial portion for sensing a first force in a medial portion of the knee and a lateral portion for sensing a second force in a lateral portion of the knee, characterised in that the relationship indicated by the knee alignment verification member (124;126) is less than 180 degrees such that the bottom surface of the distal femoral alignment assembly is less than 90 degrees relative to the femoral mechanical axis.
The system of claim 1, wherein the knee alignment verification member means includes a laser knee alignment verification member (124) coupleable to the stationary femoral portion (101) and providing a first laser beam oriented along the femoral axis of the knee and a second laser beam oriented along the tibial axis of the knee.
The system of claim 1, wherein the knee alignment verification member includes a mechanical knee alignment verification assembly (126), the mechanical knee alignment verification assembly comprising:
a knee alignment hub (127);

a first rod (128) coupleable with the knee alignment hub to be oriented along the femoral axis of the knee; and

a second rod (129) coupleable with the knee alignment hub to be oriented along the tibial axis of the knee.
The system of any one of claims 1 to 3, wherein the adjustable medial portion (102 comprises a medial paddle, and the adjustable femoral portion comprises a lateral paddle (103).
The system of any one of claims 1 to 3, wherein the position of the adjustable medial femoral portion (102) relative to the stationary femoral portion (101) is adjustable, and the position of the adjustable lateral femoral portion (103)relative to the stationary femoral portion (101) is adjustable wherein the adjustable medial femoral portion and the adjustable lateral femoral portion are optionally separately adjustable.
The system of claim 5, wherein a medial rotatable screw (107) couples the adjustable medial femoral portion (102) with the stationary femoral portion (101), and a lateral rotatable screw (108) couples the adjustable lateral femoral portion (103) with the stationary femoral portion (101).
The system of claim 6, wherein rotating the medial rotatable screw (107) adjusts the position of the adjustable medial femoral portion (102) relative to the stationary femoral portion (101), and rotating the lateral rotatable screw (108) adjusts the position of the adjustable lateral femoral portion (103) relative to the stationary femoral portion (101).
The system of any one of the preceding claims, wherein the force sensor (111) comprises a force sensing element selected from the group consisting of piezoelectric sensors, force sensing resistors, force sensing capacitors, strain gages, load cells, and pressure sensors.
The system of any one of the preceding claims, further comprising:
a processor coupled with the force sensor (111) for processing sensed force data into usable data for providing to a user; and

a visual display (117) coupled with the processor and adapted to display the usable data.
The system of claim 9, wherein the visual display (117) displays usable data representing a first force sensed in the medial portion of the knee and a second force sensed in the lateral portion of the knee.
The system of any one of the preceding claims, further comprising a plurality of locating pins (130a, 130b), and wherein the stationary femoral portion (101) defines at least one medial aperture for positioning a first at least locating pin on the distal femur and at least one lateral aperture for positioning a second at least one locating pin on the distal femur.
The system of claim 11, further comprising a cutting guide (131) removably engagable with the distal femur, the cutting guide (131) being positioned relative to the distal femur based on the position of at least one first locating pin (130a) and the at least one second locating pin (130b).
The system of claim 1, wherein the force sensor (111) is removably coupleable to a thickness adapter, the adapter configured to fill the space between the femur and tibia.
The system of claim 1, wherein the adjustable medial femoral portion (102) and the adjustable lateral femoral portion (103) include a medial fulcrum and lateral fulcrum, the fulcrums positionable against the provisionally cut distal femur when the distal femoral alignment assembly is mounted against the distal femur.
The system of claim 14, wherein a bone interface plate (137) is disposed between the fulcrums and the distal femur.